Most high-performance automobiles are equipped with disk brakes in which a disk brake rotor rotating integrally with the wheel is selectively gripped by a pair of brake pads. In order to dissipate friction heat not only from the outer surface of the disk brake rotor but also from the interior of the disk brake rotor, a plurality of radial slots are defined between the pair of friction plates which are connected to each other by a plurality of radial ribs, as disclosed, for instance, Japanese patent laid-open publication No. 52-50471. Since air flows through these radial slots at a significant flow rate due to the centrifugal force induced by the rotation of the disk brake rotor, a significant improvement in cooling efficiency may be achieved.
However, according to conventional disk brake rotors, only one of the friction plates is directly attached to the central hub while the other friction plate is attached to the one friction plate by way of radial ribs defining radial slots. According to such a structure, it is difficult to ensure the rigidity of the friction plates disposed around the central hub, and to control waviness of the friction surfaces. Such a waviness causes uneveness in the pressure between the friction surfaces and the brake pads and could lead to various undesirable consequences, such as uneven wear of the brake pads, brake shudder, and premature wear and generation of cracks in the brake pads.
Japanese utility model laid-open publication No. 63-146237 discloses a disk brake rotor comprising a central disk which is directly attached to a central hub, and a pair of friction plates which are both integrally attached to the central disk by way of radial ribs. This disk brake rotor eliminates uneveness in the thermal and stress conditions of the two friction plates, but the provision of the central disk adds to the weight of the disk brake rotor.